This invention relates generally to radio frequency identification (RFID) systems and methods, and specifically to systems and methods for two way communication among radio tags and readers using techniques that reduce interference among a number of radio tags.
The management and tracking of personnel, assets, and other objects is required in a wide variety of environments, and is often cumbersome, labor intensive, and expensive. Radio receivers and transmitters have been used for many years to identify personnel and objects in such environments. For example, many systems are known for attaching radio tags to items, such as automobiles, so that when automobiles equipped with radio tags enter a certain area, such as a toll booth area, the automobiles are automatically identified and the appropriate tolls are deducted from corresponding accounts, thereby obviating the need for drivers to stop and make payment at toll booths. Innumerable other applications for such radio tag systems have been identified, in areas ranging from inventory control to facility security to sporting event timing.
Using the vehicle identification example mentioned above, known systems typically provide an RFID "reader" for each lane of traffic. In one type of known system, such readers intentionally have a small effective coverage area to prevent signals from multiple vehicles from interfering with one another. Otherwise, multiple tags transmitting simultaneously from two or more vehicles might cause signal interference with one another, thereby impeding the reception of valid data at a reader.
Although a number of "multiple-read" systems are known for reducing the deleterious effects of collisions among multiple tag signals, none is sufficiently robust to effectively provide a multiple-read system that uses a single reader to cover an area where a large number of radio tag-equipped vehicles are entering at the same time.
It would therefore be desirable to have systems and methods that could more effectively provide the capability for reading data from multiple radio tags at essentially the same time.